1. Technical Field
The present invention—involving sheet stacking devices, and finishers furnished with the devices, that stack/store on a tray sheets carried out from, typically, an image-forming apparatus—relates to improvements in sheet storing mechanisms that orderly store sheets against a regulating stop on the tray.
2. Description of the Related Art
In general, sheet stacking devices of this sort are known broadly as devices that are provided with a loading tray forming a path break downstream of the sheet discharging port, and that stack/store onto the loading tray sheets turned out from the sheet discharging port by a sheet discharging roller. The loading tray may be configured as a stack tray that simply houses the sheets, or may be configured as a processing tray that subjects the sheets to final-stage processing.
In particular, if the loading tray is configured as a processing tray, a sheet aligning mechanism is required to load the sheets (bundle) on the tray and subject the sheets to final-stage processing such as stapling, punching, or stamping. The sheet aligning mechanism, which is thus for positioning/stacking the sheets on the tray in a predetermined position (final-stage processing position), is constituted by a regulating stop on the loading tray, against which one end (leading end or trailing end) of the sheets abuts and is thereby regulated, and conveying means for conveying the sheets toward the stop.
For example, Japanese Unexamined Pat. App. Pub. No. 2003-267622 (cf. FIG. 2 in particular) discloses a device that stacks and collates on a processing tray sheets carried out from an image forming apparatus through a sheet discharging port, and staple-binds sheet bundles stacked on the processing tray. Therein, the processing tray is provided with a stop member against which sheet ends abut and are thereby regulated, as well as a conveying member (a “paddle member” in Japanese Unexamined Pat. App. Pub. No. 2003-267622) above the processing tray, for transporting toward the stop member sheets carried in through the sheet discharging port.
Similarly, Japanese Unexamined Pat. App. Pub. No. 2006-248684 (cf. FIG. 2 in particular) discloses a sheet storing mechanism that carries out onto the processing tray sheets from the sheet discharging port, and that, with a belt member disposed above the tray to let it elevate/lower, aligns the sheets by their abutting against a regulating stop.
In either of the conventional sheet storing mechanisms disclosed in Japanese Unexamined Pat. App. Pub. Nos. 2003-267622 and 2006-248684, to align against the regulating stop sheets carried in onto the tray, the conveying means (paddle or belt member), which applies a conveyance force on the sheets, aligns them using a preset conveyance force and running time (design parameters).
In implementations in which, as described above, sheets are carried in onto a loading tray disposed downstream of the sheet discharging port and aligned in the predetermined position (final-stage processing position, etc.), a conveying rotor (roller, belt, or the like) that moves up and down in accordance with the amount of sheets loaded is provided on the tray, and by means of the rotor, sheets are abutted against the regulating stop and are thereby aligned. Any of various and diverse mechanisms, such as a roller member, a belt member, or a paddle member, is conventionally employed as the conveying mechanism, which transports sheets on the tray toward the regulating stop for positioning.
Therein, a sheet-feeding rotor that in this manner conveys a sheet on the tray toward the regulating stop halts it immediately after the sheet leading end has abutted against the regulating stop, to prevent the sheet from being damaged by being over-conveyed.
The conveyance force that the sheet-feeding rotor imparts to the sheets by is conventionally set at a defined value (design parameter). Consequently, when the material nature of the sheet surface differs the conveyance force imparted to the sheet varies, giving rise to registration or skewing problems, in which the sheets fail to reach the regulating stop reliably, or to problems of damage, such as leading-end crumpling, affecting sheets having abutted against the regulating stop.
In particular, for sheets subjected to final-stage processing, a recent trend is to use sheets differing significantly in the material nature of the surface, such as color copy sheets and monochromatic copy sheets. In such cases, mixing for example gloss paper, whose surface coefficient of friction is low, with plain paper, whose coefficient of friction is relatively large, may lead to the former not reaching the regulating stop (registration problem) or to skewing, and may lead to sheet damage such as leading end crumpling in the latter.
To solve such problems, for example, the engaging force between the sheet-feeding rotor and the sheets on the tray could be more/less adjusted. However, in a situation, for example, in which color images alternate with monochromatic images on sheet by sequentially conveyed sheet, the above-described problem cannot be solved unless the pressure-contact force of the sheet-feeding rotor is adjusted for each sheet. Accordingly, adjustment of the pressure-contact force of the sheet-feeding rotor requires complicated mechanisms and controls.